The new definition of the International System of Units (SI) of the kilogram based on a fixed numerical value of the Planck constant, one of the fundamental physical constants, came into force on May 20, 2019. AIST has measured the Planck constant with world’s highest level of precision and contributed substantially to the new definition of the kilogram by X-ray crystal density (XRCD) method with 28Si-enriched spheres. In an accurate determination of the Planck constant by the XRCD method, the surface characterization of the Si sphere is indispensable. We measured the composition and the thicknesses of the oxide and carbonaceous layer existing on the Si sphere surface by X-ray photoelectron spectroscopy (XPS) and succeeded in reducing the uncertainty caused by the surface layer in the determination of the Planck constant. This paper describes an accurate thickness measurement of the surface layer on a ²⁸Si-enriched sphere using XPS.

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We have developed a mathematical automatic estimation algorithm for deriving the ionization potential from photoelectron yield spectroscopy (PYS). The residuals between the regression line and the data obtained by the Fowler model were calculated by the mean absolute error (MAE) and the mean square root error (RMSE). The analytical range that the Fowler model can be applied is estimated by using the ratio of RMSE/MAE. The estimation was performed by this algorithm using the 87 verification datasets. The correct answer rate was improved to 79% than the conventional fitting (least square method) rate of less than 50%.

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Materials Curation^® is a method to search materials by combining scientific principles in multi-disciplinary way proposed by one of the authors. This method utilizes relations among various material properties to overcome a problem that experimental or calculation data on materials in an issue are not enough at all for big-data type analysis in machine learning. For the interdisciplinary use of scientific principles, the authors have developed a prototype of materials curation support system. Examples of relations among material properties, the concept of database of relations and searching relations, and the construction of the system including the database and searching program are described.

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The electron affinity and ionization potential of OLED materials were evaluated using low energy inverse photoelectron spectroscopy (LEIPS) and ultraviolet photoelectron spectroscopy (UPS), which can be incorporated into a multi-technique X-ray Photoelectron Spectroscopy (XPS) system. The energy level of lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) were estimated by LEIPS and UPS for three kinds of samples, i.e. CuPc (Cu phthalocyanine) thin film (10 nm) / ITO (indium tin oxide) film / glass substrate, C₆₀ thin film (10 nm) / Au film / ITO film / glass substrate, and α-NPD (Bis[N-(1-naphthyl)-N-phenyl]benzidine) thin film (10 nm) / ITO film / glass substrate, respectively. The band gap at the surface of the materials were determined by these levels. In addition, by utilizing Ar-gas cluster ion beam (Ar-GCIB), in-situ LEIPS and UPS depth profiling of interface of the multilayer films were also demonstrated.

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